The present invention relates to high service temperature block copolymers which contain polyphenylene ether resins and block copolymers of vinyl aromatic hydrocarbons and conjugated dienes. More particularly, the present invention relates to a method for making improved high service temperature block copolymer blends which can be used for rubber compounds and hot melt adhesive and sealant compositions utilizing polyphenylene ether resins and such elastomeric block copolymers.
Hot melt adhesive compositions containing polyphenylene ether resins and block copolymers of vinyl aromatic hydrocarbons and conjugated dienes are well known. In U.S. Pat. Nos. 4,104,323 and 4,141,876, the patentee describes such hot melt adhesive compositions containing low molecular weight polyphenylene ether (PPE) resins. Such low molecular weight PPEs have a molecular weight as described by intrinsic viscosity of less than 0.3 deciliters per gram. The patents also describe blends of such block copolymers and PPEs with higher viscosities, i.e. 0.3 deciliters per gram or more and show that the blends with the lower molecular weight PPEs are superior to those using the higher molecular weight PPEs.
In commercial practice, it has proved difficult to use either the blends with the high molecular weight PPE or the low molecular weight PPE in adhesive and sealant formulations. It has proved very difficult to adequately mix the PPEs with the block copolymers in commercial equipment. This is most likely due to the limitations of the equipment which is most often used by formulators who are interested in making hot melt adhesives or sealants with these materials. Such compounders and formulators normally use lower viscosity materials than PPE and thus do not require high intensity mixing apparatus.
Therefore, it would be very advantageous if a way were found to permit these high service temperature adhesive and sealant compositions to be made in the currently commercially used low intensity mixing equipment such as Sigma Blade mixers. The present invention provides such a method and allows the formulator or compounder to achieve a very. good compatible mixture of these materials while using the lower cost mixing methods which are currently being used commercially today.
The aforementioned U.S. Pat. Nos. 4,104,323 and 4,141,876 describe the advantages of utilizing lower molecular weight PPEs, i.e. the ability to achieve high service temperatures in the blends while avoiding the high viscosity which is a characteristic of the higher molecular weight PPEs. The lower molecular weight PPEs are difficult to make commercially. Therefore, it would be an advantage to find a way to make a lower viscosity high service temperature blend using the higher molecular weight PPEs. The present invention also provides such a method.